It is seen that the demand of color image formation obtained by an electrophotographic image forming apparatus typified by a laser printer or MFP (a multifunction printer; a multifunction complex printer) is further expanding. An image forming apparatus employing a single component developer, which is capable of forming an image without using a carrier, is mainly employed as a color image forming apparatus to satisfy this demand, since the downsizing and maintenance are also desired in order to spread the foregoing. As the image forming method employing a single component developer, known is a method in which a latent image formed on an electrostatic latent image carrier is transported by a developer carrier such as a developing roller, and developed by a single component developer made of a supplied toner, and the formed toner image is subsequently transferred into a transfer material to thermally fix the toner image on the transfer material.
From the viewpoint of recent toner technology trend, the development of a so-called polymerization toner prepared via a process of coagulating resin particles in an aqueous medium has actively been done. The polymerization toner is suitable for preparing particles having a small particle diameter accompanied with similar particle shape and size in the manufacturing process, and is capable of being a most suitable toner to form a pictorial image (refer to Patent Document 1, for example).
Meanwhile, with downsizing of an image forming apparatus, a downsized developing device is also to be used, whereby crushing of toner in the developing device is of particular concern since the downsized developing device gives toner a strong impact from a stirring member and a film formation member. Fine powder generated via crushing of toner adheres to the surface of a developing roller, and filming which causes scattering of toner is induced. Consequently, as a technique aiming at prevention of crushing a single component toner, there is a technique in which toner having a softening point, particle hardness and average circularity which have been identified is produced via particle formation in an aqueous medium, for example (refer to Patent Document 2, for example).
In the case of acquiring a toner constituent material to satisfy these conditions at the same time, however, kinds of a resin and so forth are to be limited, resulting in an influence on toner production cost.
Rapid full color image formation used for preparation of a conference material at the office and POP advertisement tends also to be demanded. In the case of conducting high-speed printing with a downsized color printer, rapid and stable charge rising capability is desired for toner. As a technique corresponding to this demand, there is a technique capable of enabling the rapid charge rising, by using toner made of a polyester resin, a colorant, a charge control agent or oxidation type polyolefin wax, which is prepared via kneading and crushing processes, for example (refer to Patent Document 3, for example).
However, the constituent material of the toner disclosed in above-described Patent Document 3 is also limited, and an influence on the toner production cost can not be neglected. There was also a tendency to reduce image density gradually via charging during continuous printing.
As a technique aiming at prevention of density reduction caused by continuous printing, there is a technique in which a small diameter toner having a sharp particle size distribution can be acquired by stabilizing liquid droplets of a monomer composition in an aqueous suspension medium via preparation of a polymerization toner by combining a positive charge control resin with a negative charge control resin, for example (refer to Patent Document 4, for example).
However, the influence on toner production cost could not be ignored, since the charge control resin was a specific resin in this technique.
[Patent Document 1] Japanese Patent O.P.I. Publication No. 2000-214629
[Patent Document 2] Japanese Patent O.P.I. Publication No. 2004-46117
[Patent Document 3] Japanese Patent O.P.I. Publication No. 2000-235280
[Patent Document 4] Japanese Patent O.P.I. Publication No. 2000-347445